This invention relates to dynamoelectric machines, and in particular to electric motors employing a device to change voltage applied to the motor or to change direction of motor rotation, or both.
In many applications, it is necessary or desirable to reverse the rotation of a motor, whether of split phase, capacitor start or run, or three phase designs. Interchanging one or more leads of the motor windings can produce the desired result. The lead interchange typically is accomplished on a terminal board located inside a terminal box attached to or a part of the motor housing. If the leads are not accessible from a terminal box, access to the interior of the motor may be necessary. External reversing switches are also used in some cases.
Where a terminal board is used, spaced lugs mounted to the board with lead identification marked adjacent to each lug on the board frequently are used to permit motor rotation reversal by interchanging connections between two of the lugs. Visibility and access to the lugs and their identifying markings are generally less than desirable. Unless considerable care is exercised in effecting the reversal, particularly in single phase motor designs, the effort may be time consuming or frustrating or, more importantly, wrong.
In addition to rotation reversal, it is often desirable or necessary to operate an appropriately designed motor at one or the other of two different voltages. Thus, if a motor is designed for dual voltage applications, it possible, by switching or changing winding connections, to change the operating voltage of the motor from 115 volts to 230 volts, for example. This is an important feature in many applications because a single motor may be stocked, that motor being usable in a variety of applications by field personnel.
Whether considering dual voltage operation or rotation reversal or a combination of both, care must be exercised when changing circuit connections to avoid motor damage. Typically, information regarding connections required for each operating mode are identified on the motor housing or on a cover plate overlying an internal board where connections are made and changed. Where individual connections are required to effect circuit changes, the opportunities for connection errors and motor damage increase with the number of connections required, the extent to which access to the connections are physically limited, and the amount of information regarding the making of connections that is physically available immediately adjacent to the connectors where the changes will be made.
The prior art has addressed the problem of providing easy and reliable field change of motor connections for a long time. For example, U.S. Pat. No. 4,748,355 discloses a universal motor connector unit that is usable with different three phase and single phase motors for connecting the motors to different source voltages. While the prior art in general works for its particular purpose, the present invention, unlike the prior art and the 4,748,355 patent in particular, utilizes different plug constructions for single phase and three phase applications, and thus provides an entirely different approach for a voltage change and motor reversal device, as will be explained in more detail below. By using separate plugs, visual indications of the resulting motor connection is available to the installer and end user.